Plants for transforming and melting metal charges are known, which comprise an electric arc furnace suitable to cooperate with a loading system, which can be of the continuous type, for example a conveyor belt, or discontinuous, for example with baskets. The electric furnace provides at least one container, or hearth, and a covering roof. The electrodes are introduced through holes present in the roof.
It is also known to use weighing systems, of the direct or indirect type, the latter being based for example on measuring the level of the liquid bath, so as to obtain information that is then used to control the operating parameters of the furnace.
For example, WO2005/052196, in the name of the present Applicant, describes a method in which the furnace is weighed periodically to detect the quantity of steel present in the furnace; in this method the temperature of the liquid bath is also monitored, substantially continuously, and the flow rate of the scrap unloaded inside the furnace is detected by weighing, and is regulated so that the temperature is kept constantly around a desired and predetermined value.
In other words, the value detected of the weight of the charge unloaded on each occasion into the furnace is used so as to regulate the speed of unloading and/or the quantity of scrap in the basket so as not to create disturbances, beyond a tolerated value, in the temperature of the liquid bath. This system is also used for keeping the quantity of liquid steel in the furnace under control.
Document JP 080005248, published on 12 Jan. 1996, also describes a method to control the melting process in an electric furnace, in which the weight of an electric furnace system and the weight of the charge introduced into the furnace are continuously detected and, according to the variations detected in said weights, the speed of feeding the charge into the furnace is adjusted.
Document RU 2082763 also describes a method to control the melting process in a furnace using signals arriving from a sensor of the weight of the scrap and from a sensor of the weight of additional materials which pass through a control unit.
Document U.S. Pat. No. 6,004,504, which provides a feed system of the continuous type and pre-heats the charge before it is introduced into the furnace, describes a method and an apparatus which use a detector of the mass of the charge and a detector of the loading speed, associated with the conveyor belt in order to control the unloading process of the charge into the furnace.
Document WO-A-03087688 describes a method for the production of molten metal in an electric furnace which provides to control at least three parameters, that is, the weight of the metal material loaded into the furnace, the volume of gas containing oxygen fed into the furnace and the quantity of electric energy fed to the furnace, in order to optimize the melting process.
WO-A-2006/108691 also deals with the problem of keeping a melting process under control, in an electric furnace with a continuous loading system, using information relating to the weight of the electric furnace system. WO'691 describes the use of rolls associated with the supporting elements of the hearth in which the weight sensors are disposed, which thus measure only the weight of the hearth and its content, and not that of the other associated equipment and/or equipment supporting the furnace.
WO'691, like WO'196, also provides that the signals relating to the weight of the hearth, after every cycle to unload the scrap, are correlated to the quantity of energy fed to the furnace to keep the temperature substantially constant and near the ideal value for the melting cycle.
In the field of transforming ferrous material into molten steel it is also known that there is a continuous search intended to guarantee increasingly high quality characteristics of the molten material, together with less wear and fewer risks of damage to parts and components, lower energy consumption with the same amount of molten metal, shorter cycle times and lower incidence of the costs of labor.
Purpose of the present invention is therefore to achieve an optimized weighing device for improving and making the measurement obtained more reliable and precise, and in this way to make the control of the melting process even more efficient, based on the information detected by said weighing device.
In this light, and based on long and thorough studies and experiments, Applicant has perfected the existing technologies, including those described in the documents described above, overcoming some disadvantages of the state of the art and achieving the present invention.